If they are a transexual man then wouldn't they be a woman? Legally and well.. as far as their gender is concerned they are a woman.

Pansexual means little more than attraction to any male or female, even if their sex now is different than the sex they were born with. I think it's a fine term actually. For instance I really can't imagine myself with FtM (though holy shit I have seen some cute/hot FtM who have thrown me for a loop) just saying...

To me, pansexual feels like an invented solution for an invented problem.

I don't think I would be upset if my girl kissed her best friend passionately, or any girl for that matter. A guy yes, but it just feels different for me I guess if its just another girl. Now if it happened all the time, then maybe I might start to worry she's switching teams...but as long as I was her man I don't think I would mind.

The thing here is what you two have agreed upon in your relationship. A relationship is a mutual agreement to be with a certain person for a certain value.
It really doesnt matter if either of you is pansexual, bisexual or whatever, that has nothing to do with it.
And its not like she is an animal that cant control her urges if she is pansexual. Thats like saying gay people jumps every available person he/she can.
Pansexual is just about not caring what gender it is that you fall in love/have sex with, you fall in love/have sex with the person, not its gender.

If you both had agreed that its cheating to kiss another person, then its cheating.
If you both agreed that it isnt, then its not.

It all depends on what you have agreed on. If you dont know how far you BOTH can go and what is considered ok, then you should discuss it.

IMO, it is all up to you. It is not our standards that your girlfriend should abide by, its yours. Just as you should abide by any standards she has (just to counter any argument that i'm being sexist >.>)

if it made you feel uncomfortable, then you need to confront her. imo though... this is not as bad as if she had done it to a guy. because guys become led on much more easily, which to me, is far worse than just doing something crazy with her best friend. I somehow doubt she was attempting to seduce her friend.

Jesus Christ. stop being puritan.... If you insist on the cheating... well so be it... But I tell you , you are rather puritan..
They were drinking.... They weren't sober. They had a good time, and two girls ended up exchanging a kiss. It wasn't in an enclosed environment and situation that he had zero chance to get ever aware of it. She didn't purposely set up a scenario, it was a spur of the moment.
It's a non-issue to me. We don't own other people. They are not our property.
They didn't kiss because they are in love. They kissed because they had fun and it was triggered by the comfort of a group of people having an awesome time.

So to me it is not cheating, as long as I am actually present.
The question rather is, what relationship basis actually exists here. There seem to be trust issues. That indicates a bad relationship.
If I was HER, I'd ditch him.. If you don't trust me enough, that you question my love to you. If you misread a spur of the moment, where you even took part, with me betraying you. Questioning my loyalty, then GTFO..

Who cares if it's defined as cheating or not? More importantly are you comfortable with it? If you are, then don't change anything, if you aren't then do something about it. Let her know! How important is that bit of freedom to her? Would she be willing to give that up because it makes you uncomfortable? Just how uncomfortable does it make you? Why does it make you uncomfortable, do you get jealous and/or insecure, do you have different exceptions of the relationship or relationships in general?

Kissing someone else while in a relationship isn't a crime, and in some rings it's perfectly fine to make out with other people while dating/in a relationship while it's heavily shunned in others. A lot of morally wrong or right depends on what both people agreed on and expect from a relationship.

We had a talk the next day, she's extremely sorry for doing that to me, but still doesn't consider it cheating.

If she didn't consider it cheating/wrong, then why did she wait until you left the car? She probably wasn't expecting the friends that were also in the car, to tell you what happened. Sure she can say it won't happen again next time, but if it were to occur next time, you won't find out about it because she's going to be more smart about it.

Jesus Christ. stop being puritan.... If you insist on the cheating... well so be it... But I tell you , you are rather puritan..
They were drinking.... They weren't sober. They had a good time, and two girls ended up exchanging a kiss. It wasn't in an enclosed environment and situation that he had zero chance to get ever aware of it. She didn't purposely set up a scenario, it was a spur of the moment.
It's a non-issue to me. We don't own other people. They are not our property.
They didn't kiss because they are in love. They kissed because they had fun and it was triggered by the comfort of a group of people having an awesome time.

So to me it is not cheating, as long as I am actually present.
The question rather is, what relationship basis actually exists here. There seem to be trust issues. That indicates a bad relationship.
If I was HER, I'd ditch him.. If you don't trust me enough, that you question my love to you. If you misread a spur of the moment, where you even took part, with me betraying you. Questioning my loyalty, then GTFO..

Not everybody who isn't okay with an "open relationship" is a "puritan." It's quite natural for people to like our partners to be faithful to us emotionally and physically. The fact that you don't seem to is because you are the different one. The fact that you phrased it "two girls ended up exchanging a kiss" tells me you don't understand the gravity of the behavior. She's just as interested in men as she is in women. She draws no distinction. She could have done the same thing with a guy.

The only objective way to look at this for some people who do not grasp the concept of pansexual (or bisexual) is to imagine she was kissing a guy instead of a girl. Imagine it was a guy, and ask yourself if he should be hurt? Then we pile on the fact that she told him it would NOT be okay if he kissed another girl. Yes, she thinks it's okay for her to do it, but not okay for him to do it.